The invention relates to a modulation device for a radiation detector device operable to pick up an image field. The modulation device includes a modulation disk having radial slits. The modulation disk is positioned in the plane of the image field. The modulation disk executes a nutation about the axis of the image field, and the modulation device is additionally provided with an optical system, a radiation-sensitive receiver arrangement and a signal processing circuit.
In accordance with a known modulation device, a large-area optoelectronic transducer is utilized as a radiation-sensitive receiver arrangement on which the picked-up image field is projected. This known modulation device makes it possible, in principle, to differentiate radiation sources not of interest from a radiation source to be detected, if the area of the radiation source not of interest is larger than that of the radiation source of interest, which in turn is in the order of magnitude of the slit width of a modulation disk.
By means of the modulation disk, the radiation field present within the image field is frequency-modulated.
The modulation device is used in conjunction with a position-finder and operates as follows:
The radiation of an object is transformed into frequency-modulated electrical signals dependent on the object's position coordinates and is evaluated accordingly in a signal processor. The reference system for the position coordinates is, e.g., the center of the field of view of a seeker.
The radiation-emitting object is projected on or near the modulation disk present in or near the image plane. This modulation disk is provided with radial slits to create a radial pattern having the function of modulating the detected radiation with a position-dependent code.
The radial modulation disk executes a nutation about the image field axis.
On the basis of this nutation, the rays of the beam passing through the disk are modulated with respect to their intensity. At the same time, a modulation of the sequential frequency of the pulses is carried out.
When a picture element of the image field is in the center of the image field, the pulse frequency remains constant, whereas when the picture element lies outside the image field center, a frequency deviation results which is swept at a constant modulation frequency.
The magnitude of the frequency deviation and the phase of the modulation correspond to the coordinates of the radiating object projected in the image field. In this way the movement of such a radiating object can be determined.
From DE-PS No. 27 22 018 it is known to use a liquid crystal diaphragm in the optical equipment to block out interfering radiation while allowing radiation coming from the target of interest to pass through.
Such a variable liquid-crystal diaphragm comprises raster elements arranged in a matrix form and activated by means of an electronic row/column driver. The purpose of this variable liquid crystal diaphragm with the respective electronic controls is to do scans, in addition to pure masking (window formation), or respectively to perform combined masking and scanning controls. Further, this variable liquid-crystal diaphragm permits the combined use of a scanning and masking process. This is important, in particular, when in the visual field of an observation device, several objects appear simultaneously which are to be observed and evaluated successively. In such a case, to facilitate observation of a target object, the object observed before, lying directly next to the latter, must be covered up, as it would otherwise act as an undesired interfering target.